O'Banion, B. | Search bioRxiv

bioRxiv2026

A beneficial bacteria influences myo-inositol homeostasis to protect plants during drought

Exposure to abiotic stress is one of the primary factors limiting crop productivity with drought stress is the most prevalent. Under drought, plants can produce osmolytes that increase water retention and prevent severe drought symptoms. Plant responses by extension also impact their associated root microbiomes through altered root metabolite concentrations and exudation. For example, myo-inositol (MI) serves as a precursor to osmolytes and also serves as a mediator for plant-microbe interactions in Arabidopsis thaliana (Arabidopsis). Here, we inoculated plants with Pantoea sp. R4 (R4), an isolate that can catabolize MI, and subjected them to drought. We observed that R4 colonized plants experiencing drought maintained their leaf relative water content while uninoculated planted did not, and that this colonization coincided with enrichment of MI in the shoots and depletion of MI in the roots. Interestingly, exogenous MI alone rescued water retention in wild-type Col-0, but not in int1 mutants, which lack the tonoplast MI transporter. Together, our results show that R4 colonization under drought conditions increases MI in the shoots, that this accumulation is associated with increased leaf water retention, and that INT1-mediated MI transport is required for this protection. Our results suggest that microbial colonization can alter how MI is localized in plants, which can inform future development of treatments to protect plants from drought.

microbiology↗

bioRxiv2025

Ralstonia pseudosolanacearum LOV domain protein regulates environmental stress tolerance, iron homeostasis, and bacterial wilt virulence

Ralstonia pseudosolanacearum (Rps), which causes bacterial wilt disease of many crops, must integrate environmental signals to successfully transition from soil to its pathogenic niche in host plant xylem tissue. Mutating a putative sensing/signaling gene had little transcriptomic effect on Rps strain GMI1000 in culture. However, when the mutant grew in tomato over 180 genes were differentially expressed relative to wild type. The gene was therefore named rprR for Ralstonia plant-responsive regulator. In planta, the {Delta}rprR mutant dysregulated genes for diverse traits including stress response, degradation of phenolic compounds, motility, attachment, and production of extracellular polysaccharide (EPS), which is a key bacterial wilt virulence factor. Quantifying Rps EPS by ELISA found increased levels in stems of plants infected with {Delta}rprR as compared to wild type. Functional assays showed {Delta}rprR is defective in attachment to tomato roots, colonization of tomato stems, and bacterial wilt virulence. In rich medium, {Delta}rprR formed biofilm normally, but the mutant formed less biofilm in tomato stem homogenate and in tomato xylem sap under flow. This phenotype correlates with the mutants altered expression of EPS biosynthetic genes and aberrant extracellular matrix. When grown in tomato stem homogenate, {Delta}rprR produced 57% more of the bacterial signal cyclic di-GMP (c-di-GMP) than wild type. This is consistent with the presence in RprR of predicted c-di-GMP modulating domains. Together these findings reveal that RprR, which is highly conserved across plant pathogenic Ralstonia, modulates several bacterial wilt virulence traits in response to the plant host. ImportanceMembers of the Ralstonia solanacearum species complex (RSSC) cause bacterial wilt, a globally destructive disease of market and subsistence crops. Like other plant-associated microbes, bacteria in the RSSC must integrate a complex array of biotic and abiotic signals to successfully infect plant hosts. RSSC genomes all encode an unusual protein, termed RprR, that contains multiple sensing and signaling domains, including two putative modulators of the secondary messenger c-di-GMP. Deleting RprR in Ralstonia pseudosolanacearum had a plant-dependent effect on many traits, including production of the key virulence factors biofilm and exopolysaccharide, as well as intracellular c-di-GMP levels. While c-di-GMP has been investigated in other plant pathogenic bacteria, this is the first report of its role in the RSSC. Most importantly, rprR was required for Ralstonia to effectively colonize plants and cause wilt disease. Thus, RprR is a plant-responsive sensor-regulator that controls pathogen adaptation to the host environment and virulence.

microbiology↗